This invention relates in general to electric motors and solenoids, and in particular to an improved pawl brake assembly for any electric motor or solenoid.
Many electric motors manufactured today use a pawl brake assembly to stop the movement of the rotor assembly when the motor is de-energized. Typically, in prior art brake designs when a motor is de-energized, the magnetic field generated in the stator core diminishes causing a spring in cooperative contact with the pawl brake assembly to pull the pawl brake into frictional engagement with the rotor assembly.
A disadvantage with prior art pawl brake assembly designs is that when the motor is energized, the portion of the pawl arm proximate to the motor lamination stack has excess vibrational movement. This excess movement causes the pawl arm to rattle and bump against the motor lamination stack, resulting in undesirable noise levels. Thus, there is a need in the art for a solution to the noise and metal fatigue caused by the excessive movement of the pawl arm of a pawl brake assembly.
The present invention is organized about the concept of providing an improved pawl brake assembly for use in electromechanical devices such as all electric motors or solenoids. For example, the improved pawl brake assembly may be used for braking the rotor assembly upon de-energization of the motor. The pawl brake assembly employs electromagnetic principles to reduce the noise and metal fatigue caused by the undesired excess motion of a pawl arm when a motor is energized.
In an exemplary embodiment according to the invention, the pawl brake assembly comprises a pawl arm and a brake portion in pivotal engagement with one another. The pawl arm may be composed of any metal alloy subject to the influence of a magnetic field, and the brake portion may be composed of any material such as plastic. The pawl arm may comprise a first end, a second end, and an extending trigger portion radially disposed between the first end and the second end of the pawl arm. The movement of the first end of the pawl arm is governed by pivotal contact with a fastener used to secure a bearing retainer to the stator assembly of an electric motor. The radially extending trigger portion of the pawl arm is in pivotal contact with the brake portion of the pawl brake assembly, e.g. via a pivotal groove.
To reduce noise and metal fatigue caused by excess vibration of the pawl brake assembly, a permanent magnet, e.g. a magnetic strip, is disposed on the second end of the pawl arm. When the motor is energized, sufficient magnetic attraction is established between the stator assembly and the magnetic strip to force and hold the second end of the pawl brake arm against the motor lamination stack. Significantly, the vibration common to prior art is eliminated. The absence of excess vibrational movement on this portion of the pawl brake assembly results in quiet operation of the motor.